The Senate Ethics Committee has appointed a special counsel to review allegations against Nevada Republican Sen. John Ensign, the panel announced Tuesday.

Attorney Carol Elder Bruce, a partner at K&amp;L Gates, will serve as special counsel in what the committee described as a &ldquo;preliminary investigation.&rdquo;

&ldquo;The purpose of a preliminary inquiry is to determine whether there is substantial credible evidence that a violation within the Committee&rsquo;s jurisdiction has occurred,&rdquo; Chairwoman Barbara Boxer (D-Calif.) and Vice Chairman Johnny Isakson (R-Ga.) said in a statement.

The committee did not specify the allegations, but Ensign has faced allegations that he tried to cover up an affair with the spouse of his former top aide. Ensign first acknowledged the affair with Cynthia Hampton, a campaign staff member married to administrative assistant Doug Hampton, in June 2009.

Both the Justice Department and the Federal Election Commission declined in late 2010 to pursue the allegation against Ensign.